1. Field of the Invention
The present invention relates to a method of assembling and testing in a dry dock a large-scale, heavy-weight, marine working platform structure.
2. Description of the Prior Art
A vertically movable, marine working platform structure having groundable support frames is used as an apparatus or a base for carrying out a geological survey and oil-drilling in a comparatively shallow sea area.
The vertically movable, marine working platform structure, which is shown in side elevation in FIG. 1, consists of spud cans 3, support frames 2 set up on the spud cans 3, a working platform 1 supported on the frames 2, and lift means 4 provided in the working platform 1 so as to vertically move the same.
The working platform 1 is, for example, quadrangular and 65-70 m in length of one side thereof, or substantially triangular and 65-70 m in length of one side thereof. A total weight of the working platform structure including the weight of the support frames 2 is around not less than 7000 tons.
Each of the support frames 2, which are shown in plan in FIG. 2, consists of four steel pipes 2a' of 1 m in diameter which are set up such as to form a tower-like construction having a substantially square cross section the length of each side of which is on the order of 7 m. The area of each of the spud cans 3 attached to the lower end of each support frame 2 is 130 m.sup.2, and at the time of testing, a load working on each of the spud cans 3 is as great as about 4000 tons. In order to have a dock bed bear the above-mentioned load, it is necessary that the dock bed has a pressure resistance of not less than 30 tons/m.sup.2.
The spud cans 3 are adapted to be fixed in the sea bottom 5 in FIG. 1. They require to be immovably set in the sea bottom 5 in accordance with the condition of rocks, sand and mud therein. Therefore, each of the spud cans 3 has a somewhat inclined bottom surface 3a and a tip 3b in the central portion thereof as shown in FIG. 1. The tips 3b are made of forged steel. When the marine working platform structure is lowered to the sea bottom to allow the tips 3b to be placed on rocks, the rocks are broken by the tips 3b. As a result, the working platform structure is fixed in the sea bottom firmly.
When this working platform structure is placed as it is in a dock, a great concentrated load works on the dock bed due to the downwardly bulging bottom surfaces 3a of the spud cans 3 and the tips 3b provided in the central portions thereof, so that the dock bed cannot bear the load. Consequently, it is necessary in general that a plurality of supporting pieces be inserted in bottom portions of the spud cans 3 and that the number and position of the supporting pieces be adjusted to decentralize the stress. However, it is actually difficult to insert such supporting wooden pieces in the bottom portions of the spud cans 3, and it is impossible that a load be applied uniformly to the dock bed.
Each of the support frames 2, which are adapted to support the working platform 1 such that the working platform 1 can be vertically moved, consists of a plurality of several-tens meter long frame members which are joined to one another to a height of 100 m to form a tower-like construction.
Herein, a brief explanation will be entered in connection with conventional operations for the general assemblage of a working platform structure P:
1. Initially, it is operated in the site for the general assemblage to dispose and arrange a number of supporting wooden pieces or installation planks to a height of 1 to 2 m above the ground surface in a manner such that the upper end face of the number of planks correspond to the lower end face of a working platform 1 to be mounted thereon. At the same time, installation planks are similarly disposed below each spud can 3.
2. Then, component parts or segments of an appropriate dimensional specification into which the working platform 1 was preparatively divided are mounted on the installation planks and assembled altogether by for example welding to a complete assembly of the working platform 1. A same as above is operated of the spud cans 3, at the same time.
3. As soon as operations in the above paragraph 2 are substantially accomplished, there are steps initiated to mount an initial portion of support frames 2 and the lift means 4 respectively on spud cans 3 and the working platform 1. Then, the remaining support frames 2 are mounted one over the other.
4. Operations for outfit or equipment of the working platform 1 are worked opportunely during or parallel with the operations in the above paragraphs 2 and 3.
5. Upon completion of assembling and building of support frames 2 and of outfitting, tests are conducted to lift and lower the working platform 1 by the lift means 4 to thereby accomplish whole operations. Several-meter long frame members are then joined successively in the upward direction. Such a fragmentary operation is generally carried out in a dock or on a berth or a bench. The resulting working platform structure as a whole is extremely high and has large dimensions and a large total weight. An assembling machine, for example, a crane, to be used in a place for carrying out a comprehensive assembling operation for this type of working platform structure is limited in the height and outer sizes. Therefore, the working platform and lower portions of the support frames are combined first in a dry dock, and the resulting product is floated on the surface of the sea or fixed in the sea bottom so as to additionally join to the support frames a suitable number of support frame members successively in the upward direction by using a marine crane or a quay crane. Thus, an objective working platform structure is completed.
FIG. 4 illustrates a marine working platform structure P transferred to the surface of the sea, in which a support column member is being additionally joined to one of the support frames 2 by using a marine crane 10. In this type of assembling method, it is necessary that different steps of assembling a working platform structure P be carried out in different places. This causes an increase in the assembling cost and term of works.
It is difficult to find out near the place of manufacture of a vertically movable, marine working platform structure having groundable support frames such a sea area that is suitable to install the working platform structure P therein. When a working platform structure P is installed in a sea area with bad sea bottom condition, it is even in danger of falling.
A complete, vertically movable, marine working platform structure P having groundable support frames is subjected to various kinds of tests before it has been installed actually. The tests generally include the following.
(a) Jack-up and down test:
In this test, a working platform 1 is checked as to whether it is moved smoothly in the vertical direction along the support frames 2. Also, the performance of a jack, a kind of a lift means, is tested.
(b) Strength test:
Water is injected into the working platform 1 to set a load thereon to a maximum level, and the fastening strength of jack houses 11 in which jacks 4 are provided and the working platform 1, and the connecting strength of the jack house 11 and working platform 1 are then determined.
(c) Pressure resistance test:
A test to apply a load to the spud cans 3. Thus, the pressure resistance of the spud cans 3 is determined.
As referred to above, a vertically movable, marine working platform P having groundable support frames 2 is large in size and weight and requires to be subjected to various kinds of tests after it has been assembled. A conventional method of assembling and testing a marine working platform structure P cannot be practiced in a dock because the dock bed does not have a sufficiently high pressure resistance.